In the usual methods of producing semiconducting p-type boron doped layers in semiconductor manufacturing, ordinarily two separate furnace processes are required.
In the first process a deposition is performed at a lower temperature usually 900.degree. C. to 1150.degree. C. after which a drive in step follows. This step produces a relatively thin doped layer semiconducting p-type silicon, but also is marked by the presence of silicon borides; these also conduct. If heated to higher temperatures, these borides decompose and act as a boron source which produces an uncontrolled impurity distribution in the final alloy (semiconductor). Thus the second step usually requires a chemical oxidation treatment to remove a controlled fraction of the boron that has diffused in the deposition. Moreover, borosilicates on the silicon surface are normally etched off between diffusions in an aqueous acid fluoride solution as part of the process. Thus in the normal mode of producing a p-type boron layer silicon, a controlled amount of boron inclusive of boride and borate formation is deposited and then a controlled portion of this layer is driven to a depth considerably deeper than that of the deposition. The latter diffusion is performed at higher temperature usually of the order of 1000.degree. C. to 1200.degree. C.
This process can be shortened into one process if the source doping species is limited or can be turned off after deposition and suitable control of boron concentration can be exercised during the high temperature drive-in diffusion.
It is apparent that this two furnace type method is time consuming and, because of the careful handling required, is a relatively inefficient and expensive procedure. Accordingly, a need exists for a more expeditious and practical method for circumventing the use of the two furnace process to achieve p-type diffusions in the doping of semiconductor substrates.